The present invention relates to a molded lens, a metal mold for a molded lens, a manufacturing method of a molded lens and an optical pickup device.
Prior Art 1
As a molded lens, there has been known a lens which is equipped with a first surface having a first optical surface whose outer circumference is not circular and a second surface having a second optical surface whose outer circumference is not circular, and further has one or two flat portions each being almost in parallel with a plane including an optical axis of the molded lens.
Prior Art 2
As a metal mold for a molded lens, there has been known a metal mold for a molded lens which molds a molded lens that is equipped with a first surface having a first optical surface and a second surface having a second optical surface, and has one or two flat portions each being almost in parallel with a plane including an optical axis of the molded lens.
Prior Art 3
As a manufacturing method of a molded lens, there has been known a method for manufacturing a molded lens which is equipped with a first surface having a first optical surface and a second surface having a second optical surface, and further has one or two flat portions each being almost in parallel with a plane including an optical axis of the molded lens.
Prior Art 4
There has been known an optical pickup device constituted by a semiconductor laser, a coupling lens, a mirror and an objective lens all arranged in this order from the light source side wherein the coupling lens including a collimator lens which converges divergent light into mostly parallel light has a first surface having a first optical surface and a second surface having a second optical surface both arranged in this order from the light source side, and a flat portion that is almost in parallel with a plane including an optical axis is not provided, and an outer flank of the optical pickup device is circular.
However, as a problem awaiting solution in (Prior art 1), it is demanded, when applying as a coupling lens of an optical pickup device for example, that a precision of astigmatism is not more than 0.02 (or 0.03) xcexrms in terms of transmission wavefront aberration. Incidentally, xcex is a wavelength of a semiconductor laser representing a light source, and when an optical information recording medium is DVD, for example, xcex equals 650 nm, while, in the case of CD, xcex equals 780 nm. If a flat portion is provided on an optical surface of each of a first surface and a second surface of a molded lens, an internal strain generated in the course of molding process makes it difficult to satisfy the demanded precision stated above, which is a problem.
A first object of the invention is to provide a molded lens which is small in size in the direction perpendicular to an optical axis, and has an excellent optical precision and less astigmatism in particular.
As a problem awaiting solution in (Prior art 2), it is difficult for a metal mold for a molded lens having a flat portion that is almost in parallel with a plane including an optical axis of the molded lens to manufacture a highly accurate molded lens.
A second object of the invention is to provide a metal mold which is for a molded lens and can mold easily a molded lens that is small in size in the direction perpendicular to an optical axis, and is highly accurate and excellent in terms of astigmatism, in particular.
As a problem awaiting solution in (Prior art 3), it is difficult to mold accurately a molded lens having a flat portion that is almost in parallel with a plane including an optical axis of the molded lens, because a part of an optical surface has a straight portion, which is a problem.
A third object of the invention is to provide a manufacturing method for a molded lens that can mold a molded lens that is small in size in the direction perpendicular to an optical axis, and is highly accurate and excellent in terms of astigmatism, in particular.
As a problem awaiting solution in (Prior art 4), a height of a coupling lens for a light source used for an optical pickup device in the direction perpendicular to an optical information recording medium is great and a height of the whole optical pickup device is also great accordingly, which is a problem.
A fourth object of the invention is to provide an optical pickup device equipped with a coupling lens that is low in terms of a height in the direction perpendicular to an optical information recording medium and is highly accurate.
The first object of the invention mentioned above is attained by either one of the following structures.
(1) A molded lens provided with a first surface having a first optical surface and a second surface having a second optical surface being located on the opposite side of the first surface, wherein a first flat portion that is almost in parallel with a plane including an optical axis of the molded lens is provided and an outer circumference of the first optical surface is circular, or, the first flat portion is provided and further a second flat portion is provided to be positionally symmetrical with the first flat portion about the aforesaid plane and the outer circumference of the first optical surface is circular.
(2) A molded lens provided with a first surface having a first optical surface and a second surface having a second optical surface being located on the opposite side of the first surface, wherein a first flat portion that is almost in parallel with a plane including an optical axis of the molded lens is provided and optical error in at least the course of molding process is corrected on the aforesaid first optical surface, or, the first flat portion is provided and further a second flat portion is provided to be positionally symmetrical with the first flat portion about the aforesaid plane and optical error in at least the course of molding process is corrected on the aforesaid first optical surface.
The second object of the invention mentioned above is attained by either one of the following structures.
(3) A metal mold for a molded lens provided with a first surface having a first optical surface and a second surface having a second optical surface being located on the opposite side of the first surface, wherein the metal mold molds a molded lens in which a first flat portion that is almost in parallel with a plane including an optical axis of the molded lens is provided and an outer circumference of the first optical surface is circular, or, a molded lens in which the first flat portion is provided and further a second flat portion is provided to be positionally symmetrical with the first flat portion about the aforesaid plane and the outer circumference of the first optical surface is circular.
(4) A metal mold for a molded lens provided with a first surface having a first optical surface and a second surface having a second optical surface being located on the opposite side of the first surface, wherein the metal mold molds a molded lens in which a first flat portion that is almost in parallel with a plane including an optical axis of the molded lens is provided and at least optical errors in the course of molding process are corrected on the first optical surface, or, a molded lens in which the first flat portion is provided and further a second flat portion is provided to be positionally symmetrical with the first flat portion about the aforesaid plane and at least optical errors in the course of molding process are corrected on the first optical surface.
The third object of the invention mentioned above is attained by either one of the following means.
(5) A manufacturing method of a molded lens wherein the molded lens described in (1) is molded by the metal mold for a molded lens described in (3).
(6) A manufacturing method of a molded lens wherein the molded lens described in (2) is molded by the metal mold for a molded lens described in (4).
The fourth object of the invention mentioned above is attained by the following means.
(7) An optical pickup device composed of a semiconductor laser, a coupling lens, a mirror and an objective lens all arranged in this order from the light source side wherein the coupling lens is the molded lens described in (1) or (2), and the first flat portion that is almost in parallel with a plane including an optical axis of the molded lens is mostly in parallel with an image forming surface of the optical information recording medium located at the position where the optical system forms an image.